Printed circuit boards have many openings which must be drilled at precise locations. In volume production, this is accomplished by computer-controlled automatic drilling machines in which the printed circuit boards are held on a tooling plate positioned on a movable work table. The work table is moved horizontally beneath a drill spindle so that upon movement of the drill through a vertical stroke the openings in the circuit boards may be drilled at proper locations. This is a very rapid and satisfactory procedure for mass production of printed circuit boards. However, many printed circuit boards require the drilling of openings of more than one diameter, some needing openings of several different sizes. This leads to inefficiency in the drilling operation because the machines must be stopped to change drills for the drilling of the different sized openings. The result is a loss of time and therefore an increase in operating expenses.
Drill changing has been facilitated by positioning a collar on the drill shank at a known distance from the tip of the drill. The collar is engaged with the end of the collet, which thereby properly locates the tip of the drill with respect to the collet to coordinate with the stroke of the spindle. This has not alleviated the problem of stopping the machine for manually changing drills, however.